Disturbed,
I think as a minimum you need to have a popcorn machine, an ice machine, a drink dispenser and a Point of sale system. Prizes on these vary a lot, depending on your requirements and budget.
Jay

The main purchases you need to make are a popcorn machine and an ice machine. If you sign an agreement with Coke or Pepsi, they will provide your equipment as long as you buy the product from them. Unless you're talking about a large operation, you can get away with a small cash register for your point of sale equipment. Popcorn machines can be purchased used for a reasonable amount of money. New ones will be considerably higher. Hope this helps.

You've asked a fairly generic question. Aside from the obvious (pop, popcorn), there's no real good answer for it & we're all pretty much shooting in the dark.

Why not visit other theatres in your area, and make up a list of what they're selling? Adjust the list to suit your tastes, and what you feel your customers will buy, then get whatever dispensing equipment you need.

As has been mentioned here, free (or loaned) equipment is available for some products. Pop, pretzels, some coffee/chocolate brands and some cookies come to mind. You'll probably have to pay for your own popcorn machine. The price will vary, depending on what size your theatre winds up being (you didn't say). Some concession companies have used machines you could look into.

If you're going to do any major food prep (cooking), you'll be buying that gear... grill, fryers, pizza ovens, product warmers, any required vent hoods. You don't find a lot of that at indoor theatres though.